1. Field of Invention
The present invention relates to displays, and more particularly to 3D displays and HDR displays using bandpass filters.
2. Discussion of Background
Methods for 3D stereoscopic projection include Anaglyph, Linear Polarization, Circular Polarization, Shutter Glasses, and Spectral Separation. Anaglyph is the oldest technology, and provides left/right eye separation by filtering the light through a two color filter, commonly red for one eye, and cyan for the other eye. At the projector, the left eye image is (commonly) filtered through a red filter, and the right image filtered through a cyan filter. The eyewear consists of a red filter for the left eye, and a cyan filter for the right eye. This method works best for black and white original images, and is not well suited for color images.
Linear Polarization 3D provides separation at the projector by filtering the left eye through a linear polarizer (commonly) oriented vertically, and filtering the right eye image through a linear polarizer oriented horizontally. The eyewear consists of a vertically oriented linear polarizer for the left eye and a horizontally oriented polarizer for the right eye. The projection screen must be of the polarization preserving type, commonly referred to as a “silver screen” because of its distinctive color. Linear Polarization allows a full color image to be displayed with little color distortion. It has several problems, these include the need for a silver screen which is expensive, fragile, and not uniform. Another problem is that the viewer must keep his head oriented vertically to avoid crosstalk from one eye to another.
Circular Polarization 3D was invented to address the problem of requiring the viewer to keep his head oriented vertically. Circular Polarization provides separation at the projector by filtering the left eye image through a (commonly) left handed circular polarizer, and filtering the right eye image through a right handed circular polarizer. The eyewear consists of a left handed circular polarizer for the left eye and a right handed circular polarizer for the right eye. A silver screen is also needed for this approach.
Shutter Glasses provides separation by multiplexing the left and right images in time. A filter for separation at the projector is not required. The eyewear consists of Shutter Glasses. These are active glasses that electronically shutter the lens in synchrony with the projector frame rate. The left eye image is first displayed, followed by the right eye image etc. Since having a direct wired connection to the Glasses in a theatre is impractical, a wireless or infrared signaling method is used to provide a timing reference for the left/right eye shuttering. This method requires an IR or RF transmitter in the auditorium. The Shutter Glasses are expensive and hard to clean, require batteries that must be frequently replaced, and are limited in their switching rate. Shutter glasses are only practical for use with D-Cinema or other electronic projection systems since very few film projectors provide the signal required to synchronize the shutter glasses with the frame rate. The method does not require a silver screen.
Spectral Separation provides separation at the projector by filtering the left and right eye spectrally. The system differs from anaglyph in that the filters for the left and right eye each pass a portion of the red, green, and blue spectrum, providing for a full color image. The band pass spectrum of the left eye filter is complementary to the band pass spectrum of the right eye filter. The eyewear consists of filters with the same general spectral characteristics as are used in the projector. While this method provides a full color image, it requires color compensation to make the colors in the left and right eye match the colors that were present in the original image, and there is a small reduction in the color gamut compared to the gamut of the projector.
All of the above methods for providing left/right eye separation for a 3D Stereoscopic presentation can be used with either two projectors (one for the left eye and one for the right eye), or may be used with a single D-Cinema projector system. In the dual projection system, the projection filter is usually static, and is located in front of the projection lens. In a single D-Cinema projector system, the left and right images are time multiplexed. Except for the Shutter Glasses case where no projection filters are required, this means that the projection filters must change at the L/R multiplex frequency. This can be done with either a filter wheel in the projector synchronized to the multiplex frequency, or with an electronically switched filter.
Dynamic range is the ratio of intensity of the highest luminance parts of a scene and the lowest luminance parts of a scene. For example, the image projected by a video projection system may have a maximum dynamic range of 500 or 600:1.
In contrast, the human visual system is capable of recognizing features in scenes which have very high dynamic ranges. For example, a person can look into the shadows of an unlit garage on a brightly sunlit day and see details of objects in the shadows even though the luminance in adjacent sunlit areas may be thousands of times greater than the luminance in the shadow parts of the scene. To create a realistic rendering of such a scene can require a display having a dynamic range in excess of 1000:1. The term “high dynamic range” has generally been equated to means dynamic ranges of 800:1 or more.
Modern digital imaging systems are capable of capturing and recording digital representations of scenes in which the dynamic range of the scene is preserved. Computer imaging systems are capable of synthesizing images having high dynamic ranges.
However, current display technology is not capable of rendering images in a manner which faithfully reproduces high dynamic ranges.
Blackham et al., U.S. Pat. No. 5,978,142 discloses a system for projecting an image onto a screen. The system has first and second light modulators which both modulate light from a light source. Each of the light modulators modulates light from the source at the pixel level. Light modulated by both of the light modulators is projected onto the screen.
Gibbon et al., International Application No. PCT/US01/21367 discloses a projection system which includes a pre modulator. The pre modulator controls the amount of light incident on a deformable mirror display device. A separate pre-modulator may be used to darken a selected area (e.g. a quadrant).
Whitehead et al., U.S. Pat. No. 7,413,307 provides high dynamic range displays capable to 800:1 and greater contrast ratio.
Despite the plurality of technologies for reproducing and displaying images, there exists a need for cost effective displays capable of reproducing a wide range of light intensities in displayed images including displays with HDR and/or 3D capabilities.